Popular smoking articles, such as cigarettes, have a substantially cylindrical rod shaped structure and include a charge, roll or column of smokable material such as shredded tobacco (e.g., in cut filler form) surrounded by a paper wrapper thereby forming a so-called “tobacco rod.” Normally, a cigarette has a cylindrical filter element aligned in an end-to-end relationship with the tobacco rod. Typically, a filter element comprises plasticized cellulose acetate tow circumscribed by a paper material known as “plug wrap.” Certain cigarettes incorporate a filter element having multiple segments, and one of those segments can comprise activated charcoal particles. Typically, the filter element is attached to one end of the tobacco rod using a circumscribing wrapping material known as “tipping paper.” It also has become desirable to perforate the tipping material and plug wrap, in order to provide dilution of drawn mainstream smoke with ambient air. A cigarette is employed by a smoker by lighting one end thereof and burning the tobacco rod. The smoker then receives mainstream smoke into his/her mouth by drawing on the opposite end (e.g., the filter end) of the cigarette.
The tobacco used for cigarette manufacture is typically used in a so-called “blended” form. For example, certain popular tobacco blends, commonly referred to as “American blends,” comprise mixtures of flue-cured tobacco, burley tobacco and Oriental tobacco, and in many cases, certain processed tobaccos, such as reconstituted tobacco and processed tobacco stems. The precise amount of each type of tobacco within a tobacco blend used for the manufacture of a particular cigarette brand varies from brand to brand. However, for many tobacco blends, volume expanded or “puffed” tobacco makes up a portion of the blend. See, for example, Tobacco Encyclopedia, Voges (Ed.) p. 419 (1984), Browne, The Design of Cigarettes, 3rd Ed., p.50 (1990) and Tobacco Production, Chemistry and Technology, Davis et al. (Eds.) (1999).
It is generally desirable to expand the volume of tobacco material, particularly cut filler, in order to increase filling capacity such that reduced weights of tobacco are incorporated into smoking articles. Certain processes directed toward increasing the filling capacity of tobacco have incorporated steam as a process component. See, for example, U.S. Pat. No. 3,529,606 to de la Burde; U.S. Pat. No. 4,4418,706 to Kim; U.S. Pat. No. 4,235,249 to Psaras; U.S. Pat. No. 4,407,306 to Hibbits; U.S. Pat. No. 4,211,243 to Ohno; U.S. Pat. No. 4,298,012 to Wochnowski; U.S. Pat. No. 4,414,987 to Utsch; U.S. Pat. No. 4,458,700 to Keritsis; U.S. Pat. No. 4,459,100 to de la Burde; U.S. Pat. No. 4,523,598 to Weiss; U.S. Pat. No. 4,687,007 to Denier; U.S. Pat. No. 4,693,264 to Hedge; U.S. Pat. No. 4,697,604 to Brown; and U.S. Pat. No. 4,844,101 to Hirsch. A number of known methods for expanding tobacco material involve impregnation of a tobacco material with volatile organic or inorganic compounds, such as halogenated hydrocarbons, iso-pentane, propane, ammonium carbonate or carbon dioxide (CO2). See, for example, U.S. Pat. No. 3,524,451 to Fredrickson; U.S. Pat. No. 3,771,533 to Armstrong et al; U.S. Pat. No. 4,310,006 to Hibbits; U.S. Pat. No. 4,340,073 to de la Burde et al; U.S. Pat. No. 4,460,000 to Steinberg; U.S. Pat. No. 4,531,529 to White et al; U.S. Pat. No. 4,561,453 to Rothchild; U.S. Pat. No. 4,760,854 to Jewell; U.S. Pat. No. 5,095,922 to Johnson et al; and U.S. Pat. No. 5,095,923 to Kramer; and EPO 514860. Certain tobacco expansion processes have been designated as G-13, G-13C and Impex. The impregnated tobacco is subjected to a heat treatment process that rapidly vaporizes the impregnating compound, thereby expanding the strands of impregnated tobacco. Expansion processes involving the treatment of tobacco impregnated with solid CO2 with heat are generally referred to in the art as dry ice expanded tobacco processes or “DIET” processes. Exemplary DIET processes are disclosed in U.S. Pat. No. 5,259,403 to Guy et al. and U.S. Pat. No. 5,908,032 to Poindexter et al; which are incorporated herein by reference.
Certain expansion processes that involve impregnating tobacco with expansion agents or compounds involve added process complexity and cost resulting from the need to impregnate the tobacco with those expansion agents and compounds. Such expansion processes typically require separate vessels designed to intimately mix the tobacco with the impregnating compound. In the case of the DIET process, the process apparatus must also be capable of withstanding pressure changes associated with the conversion of liquid CO2 to dry ice following impregnation. Thus, it would be desirable to provide a simple and cost-effective tobacco expansion process that does not require impregnation of the tobacco material with an expansion agent or compound, such as CO2.